Synergism between cocaine and atropine at the caudal ventrolateral medulla of cats.

We have previously reported that the anticholinergic properties of cocaine may be important in cocaine induced apneusis. We have studied the effects of the cholinergic muscarinic antagonist atropine (ATR) on cocaine induced apneusis at the caudal chemosensitive areas of the ventrolateral medulla oblongata (CVLM). Experiments were performed in urethane anesthetized and tracheotomized cats with the CVLM surgically exposed. Topical application of ATR (44 mM ) to the CVLM produced significant decrements in minute ventilation (V(E)) and mean arterial blood pressure (MABP) (P<0.05) but the effects on tidal volume (V(T)), respiratory frequency (f) and heart rate (HR) were not significant. Administration of cocaine (37 mM) to ATR pretreated animals increased the incidence of cocaine induced respiratory arrest to more than twofold greater than when cocaine was administered in the absence of pretreatment. The ATR pretreated animals that did not experience inspiratory arrest after cocaine were shown to exhibit significant decrements in f and V(E) as a consequence of prolonged inspiratory pauses. The reduction in MABP after cocaine in ATR pretreated animals was also significant. These results suggest that ATR enhances the central respiratory toxicity of cocaine by acting synergistically at CVLM chemosensitive sites.

Decreased CSF pH at ventral brain stem induces widespread c-Fos immunoreactivity in rat brain neurons.

Physiological evidence has indicated that central respiratory chemosensitivity may be ascribed to neurons located at the ventral medullary surface (VMS); however, in recent years, multiple sites have been proposed. Because c-Fos immunoreactivity is presumed to identify primary cells as well as second- and third-order cells that are activated by a particular stimulus, we hypothesized that activation of VMS cells using a known adequate respiratory stimulus, H(+), would induce production of c-Fos in cells that participate in the central pH-sensitive respiratory chemoreflex loop. In this study, stimulation of rostral and caudal VMS respiratory chemosensitive sites in chloralose-urethane-anesthetized rats with acidic (pH 7.2) mock cerebrospinal fluid induced c-Fos protein immunoreactivity in widespread brain sites, such as VMS, ventral pontine surface, retrotrapezoid, medial and lateral parabrachial, lateral reticular nuclei, cranial nerves VII and X nuclei, A(1) and C(1) areas, area postrema, locus coeruleus, and paragigantocellular nuclei. At the hypothalamus, the c-Fos reaction product was seen in the dorsomedial, lateral hypothalamic, supraoptic, and periventricular nuclei. These results suggest that 1) multiple c-Fos-positive brain stem and hypothalamic structures may represent part of a neuronal network responsive to cerebrospinal fluid pH changes at the VMS, and 2) VMS pH-sensitive neurons project to widespread regions in the brain stem and hypothalamus that include respiratory and cardiovascular control sites.

Somatosensory evoked potential, neurological examination and magnetic resonance imaging for assessment of cervical spinal cord decompression.

The present study was designed to determine the relationship between neurological testing, anatomical imaging, and electrophysiological monitoring for assessing outcome of cervical spinal cord decompression. We prospectively studied 28 consecutive patients (age 39-76 yr) who were subjected to presurgical-(1-3 wk) and postsurgical (3-4 mo) neurological examination and recording of the median nerve somatosensory evoked potential (SEP). In 13 patients, magnetic resonance imaging (MRI) was also performed. Changes in neurological function, SEP and MRI were evaluated and graded as (1) improvement,(2) no change or (3) deterioration. Neurological outcome (NO) was based on changes in motor grade strength, sensory, reflexes and gait. The SEP outcome was based on changes in latency and disappearance of SEP waveform components whereas MRI evaluation was based on changes in spinal cord and canal diameters. Significance of association between NO, SEP and MRI was determined by Pearson's Chi-Square statistic (P<.05). The SEP improved in 71% (20/28) and deteriorated in 28% (8/28) of the subjects. An association between SEP changes and NO was found in 82% (23/28) of the subjects (P = .0038). Decompression increased the spinal canal diameter in 92% (12/13), and the spinal cord diameter in 38% (5/13) of the subjects. An association between NO, or SEP and MRI was not detected. Changes in median nerve SEP latency appear to be predictive of the neurological status of patients subjected to cervical spinal cord decompression. Postoperative increments in SEP latency or disappearance of the SEP waves were indicative of poor outcome after surgical decompression of the cervical spinal cord.

Analgesic responses to intrathecal morphine in relation to CSF concentrations of morphine-3,beta-glucuronide and morphine-6,beta-glucuronide.

This study was performed to determine whether variations in analgesic responses to intrathecal morphine could be explained by cerebrospinal fluid (CSF) concentrations of morphine metabolites. Twenty-four CSF samples were collected at the beginning, middle and end of treatment periods in seven cancer patients with pain of malignant origin. CSF concentrations of morphine-3,beta-glucuronide (M3G) and morphine-6,beta-glucuronide (M6G) metabolites were measured by gas chromatography/mass spectrometry. Analgesic responses to morphine were estimated concurrent with CSF collection using a visual analog scale representing percentages of pain relief. Effective analgesia was defined as > or = 75% pain relief. CSF concentration of M3G and M6G in the 24 samples were 722 +/- 116 ng/ml and 699 +/- 158 ng/ml, respectively. CSF samples were categorized into two groups: (1) those collected during effective analgesia (N=14), and (2) those collected during ineffective analgesia (N=10). M6G levels detected in group 1 samples (effective analgesia) were significantly greater than those found in group 2 samples (ineffective analgesia) (978 +/- 243 ng/ml vs 309 +/- 68 ng/ml, P<0.05). Intergroup differences in CSF M3G concentrations and M3G/M6G ratios were not significant. It is concluded that CSF M6G may be indicative of effectiveness of analgesia in cancer patients subjected to intrathecal morphine.

Growth inhibition of subcutaneously transplanted hepatomas without cachexia by alteration of the dietary arginine-methionine balance.

Previous studies have shown that alteration of the dietary arginine-methionine balance by use of synthetic L-amino acids inhibits tumor growth of a subcutaneously transplanted Morris hepatoma at the expense of maintaining body weight. However, L-methionine is susceptible to degradation and, therefore, may contribute to a deficiency state. The present studies were performed to determine whether growth of subcutaneous hepatoma transplants is inhibited, and body growth maintained, when rats are fed diets containing L-methionine in replacement of N-acetyl-L-methionine (NALM) for 28 days. Tumor-free and tumor-bearing rats fed a control diet, with amino acids replacing protein, had gains in body weight: 31.3 +/- 1.0 and 19.1 +/- 0.5 g (12% and 7%), respectively. Rats fed six experimental diets, with varying L-arginine-NALM balances, had body weight gains ranging from 18.4 +/- 0.3 to 26.7 +/- 0.9 g (7-10%). Tumor weight of control rats was 10.65 +/- 0.24% of body weight. Diets supplemented with L-arginine in combination with normal and deficient NALM decreased tumor weights by 35% and 38%, respectively, It is concluded that dietary replacement of L-methionine with NALM and supplementation with L-arginine inhibits growth of a subcutaneously transplanted Morris hepatoma in the absence of cachexia.

Cardiorespiratory effects of cocaine and procaine at the ventral brainstem.

The caudal ventrolateral medulla (CVLM) is an area of the brainstem, in the vicinity of the hypoglossal nerve roots, where cholinergic and adrenergic neurons participate in respiratory and vasomotor control. Cardiorespiratory depression has been produced by topical application of cocaine to the CVLM. In the present studies, the effects of topical pretreatments of the CVLM with alpha-adrenergic blockers (prazosin 4.8 mM) and beta-adrenergic blockers (propranolol 11.3 mM) on the cardiorespiratory responses to topically administered cocaine (37 mM) were investigated in urethane anesthetized cats. Both prazosin and propranolol failed to produce ventilatory responses and to counteract cocaine-induced apneustic breathing. However, the cocaine-induced decrement in mean arterial blood pressure (MABP) following pretreatment of the CVLM with propranolol was found to be 11 +/- 5%, compared to the 18 +/- 5% decrement produced by cocaine alone. These differences were not statistically significant. Procaine (37 mM) in equimolar doses to cocaine, produced a small statistically significant decrement in MABP (P < 0.05) without ventilatory effects. Topical administration of procaine (73.3 mM), at approximately twice the equimolar dosage of cocaine, produced apneustic breathing that was indistinguishable from that produced by cocaine. The neurotoxic properties of cocaine that produce apneustic breathing appear to be similar to that produced by the anesthetic agent procaine, and the alpha- and beta-adrenoceptor blockers prazosin and propranolol do not appear to antagonize the vasomotor depression induced by cocaine at the CVLM.

Monitoring of median nerve somatosensory evoked potentials during cervical spinal cord decompression.

We evaluated the intraoperative utility of monitoring median nerve somatosensory evoked potentials (SEPs) in 31 consecutively hospitalized neurosurgical patients (mean age 55.3 +/- 2.1 years) who underwent spinal cord decompression for cervical herniated disc, spondylosis, or tumor. Pre- and postoperative standard neurological examinations included evaluation of motor function, sensory responses, gait, tone, and reflexes. Evoked potentials were recorded from clavicular Erb's (N9) and contralateral cortical (N20) points. Intraoperatively, SEP measurements were obtained after the onset of anesthesia (baseline control) and were repeated throughout the operative procedures. N20 and N9-N20 conduction latencies were measured for each SEP recording; disappearance of the SEP waveform was interpreted as a nonquantifiable increase in latency. Follow-up neurological examinations were made immediately after and up to 6 months following surgery. Postoperatively, the 31 study subjects were assigned to one of two groups based on neurological evaluation: 27 group I subjects had either no change or improvement (good outcome) whereas four group II subjects had postoperative neurological deterioration (poor outcome). Intraoperative N9-N20 interpeak latency was found to increase during cervical decompression in six of 27 group I and in two of four group II subjects. Only two of the Group I subjects exhibited increases > 10% (14 and 19%, respectively). Intraoperative communication to the surgeon of a marked increase of N9-N20 latency during positioning for cervical traction clearly obviated a poor outcome in one group I subject; Upon removal of traction, latency decreased and significant changes in neurological function were not detected postoperatively. The SEP waveform disappeared in two of the group II and in none of the group I subjects. In the two group II subjects exhibiting increases of N9-N20 latencies, increments were > 20%. These findings indicate that in patients undergoing cervical spinal cord decompression, disappearance of SEPs or increases > 20% in the N9-N20 interpeak latency are suggestive of operative conditions that place patients at risk for poor neurological outcome.

Effects of a stroma-free hemoglobin and perfluorochemical combination on ultrastructure and function of the isolated rat kidney.

Experimental perfusions of isolated rat kidneys were performed with flow rates adjusted to produce comparable glomerular filtration rates (GFR) in control and experimental groups. The experimental perfusate, consisting of Krebs-Ringer bicarbonate (KRB) containing 3.5% (uncrosslinked) stroma-free hemoglobin (SFH) plus 3.5% of the perfluorochemical (PFC) Fluosol-DA, was found to produce only 48% as much urine as the control perfusate consisting of KRB containing 7% dextran (without either SFH or PFC). Perfusion with the experimental SFH/PFC mixture was associated with mean fractional reabsorptions of sodium 3.3% greater and of potassium 5.1% lesser than perfusion with the control KRB (with dextran) solution (p < .05). The SFH/PFC mixture was localized histochemically to the capillaries and urinary spaces of glomeruli; and to the apical microvilli, basal laminae, and intracytoplasmic vacuoles of proximal renal tubular cells. Since the glomerular filtration rate was not a factor, decremental urine production appears to be associated with increased reabsorption of sodium, excretion of potassium, and proximal tubular uptake of the experimental SFH/PFC mixture by endocytosis.

Acute beneficial effect of Fluosol-DA on urinary excretion of stroma-free hemoglobin in the isolated rat kidney.

In a timed study over 75 min, divided into 5 15-min periods, experimental perfusions of isolated rat kidneys using Krebs-Ringer bicarbonate (KRB) containing 3.5% (uncrosslinked) stroma-free hemoglobin (SFH) plus 3.5% of the perfluorochemical Fluosol-DA were found to excrete only 13% as much total hemoglobin (Hb) as control perfusions using KRB containing 7% SFH alone (controls). The glomerular filtration rate was the same for experimentals and controls in 3 periods, and slightly higher in the experimentals in 2 periods. However, urine flow was found to be significantly decreased in all 5 periods for the experimentals relative to the controls. These effects can be explained by reabsorption of glomerular filtrate containing Hb by endocytosis of renal tubular cells.

Effects of cholinomimetics on cocaine-induced hypotension and apneusis at a ventral brainstem cardiorespiratory control site.

The current study was undertaken to evaluate the effects of cholinomimetic drugs on cocaine-induced central cardiorespiratory depression. Cats anesthetized by urethane (2.0 g/kg) were subjected to topical application at the caudal ventrolateral medullary surface (cVMS) of cocaine and two cholinomimetic pretreatment drugs. The following drug regimens were tested: 37 mM cocaine 1) given alone; 2) given 5 min after 2.7 mM carbachol pretreatment; and 3) given 5 min after 3.6 mM physostigmine pretreatment. In 7 of 11 cats, pretreatment with physostigmine decreased the incidence of cocaine-induced apneusis and hypoventilation significantly (p < 0.05); these animals showed no significant change in the mean arterial blood pressure during the 5-min pretreatment before administration of cocaine. In 4 of 11 cats, the physostigmine pretreatment produced a significant decrease in mean arterial blood pressure followed by lethal cardiorespiratory arrest when cocaine was administered. Pretreatment with carbachol resulted in cardiorespiratory responses which were not significantly different from those produced by cocaine alone. In anesthetized cats not exhibiting hypotensive responses to physostigmine, pretreatment may ameliorate cocaine-induced respiratory failure by ventral brainstem control mechanisms.

Central cocaine neurotoxicity at brainstem cardiorespiratory control sites.

Cocaine hydrochloride was applied topically to the ventrolateral medullary surface (VMS) where chemosensitive respiratory and vasomotor control sites are colocalized. Cats (n = 16) were anesthetized with urethane (2.0 g/kg, 80 percent of dose titrated over 60 min). The trachea of each animal was cannulated and the VMS was surgically exposed. Tidal volume (VT), frequency of breathing (f), systolic and diastolic blood pressure (SBP and DBP, respectively), and heart rate (HR) were measured. Cocaine (62.5 micrograms per site) administered at the VMS control sites decreased f, SBP, and DBP significantly (p < 0.05), without changing HR or VT values. This cocaine-induced hypoventilation was associated with brief intervals of inspiratory cramp (apneusis). Central cocaine neurotoxicity may result from interaction of cocaine with VMS sites, producing increased inspiratory drive and decreased vasomotor tone.

Ca2+ antagonists and db-cAMP sustain a rise in renal blood flow induced by acetylcholine in indomethacin-treated dogs.

Renal arterial infusion of acetylcholine (ACh) in the dog normally produces a sustained rise in sodium excretion (UNaV) and in renal plasma flow (RPF). When prostaglandin (PG) synthesis is inhibited, ACh induces only a transient increase in UNaV and RPF followed by a progressive decline in UNaV and RPF, and a rise in renin secretory rate (RSR). Renal arterial infusion of PGE2 but not a vasodilator such as bradykinin restored the response to ACh to normal in indomethacin (Indo)-treated dogs. During renal arterial infusion of dibutyryl cyclic AMP (6 mg/min), ACh also produced a sustained increase in UNaV and RPF despite an inhibition of PG synthesis by Indo. Renal arterial infusion of verapamil (60 micrograms/min) or diltiazem (60 micrograms/min) also prevented the subsequent fall in RPF when ACh was infused; RSR, however, did not show a rise. The results suggest that synthesis of PGE2 with stimulation of cAMP is required for sustained ACh action. When PGE synthesis is inhibited, ACh may produce renal vasoconstriction by increasing intracellular Ca2+ concentration. The partial effect of calcium channel blockers suggests that release of calcium from intracellular stores as well as calcium entry may mediate the response.